You are here

Caves of the Mellte Valley Update

I have decided to include some of the obscure or updated/new surveys. Help reinvestigating the sites I still haven't looked at gratefully received. I am currently working in Cwm Porth woods and the surrounding area and some interesting new features have been thrown up.. I would like also to include photos of the entrances..

Key:

(S) - Sinks

(R) - Risings

(U) - Unconformity Caves

(O) - Other

1. PWLL DERW (S) (U)

Alt Name: Pwll Derwen (in error)

NGR SN 94117 12389

An impressive sink in the forestry land just to the north of the Mellte Castle - Penderyn Road reached by a stile over the forestry fence. The forest around this massive shakehole has been cleared (2006) and it can be seen clearly from the road. A fairly large perennial stream runs off the gritstone moors into a huge steep-sided doline and sinks amongst massive gritstone boulders on its western side. Although many groups have dug this site including Croydon CC in the past, the most committed attention has been from a team led by Jon Jones. This strongly draughting scaffolded dig penetrates the boulders of this shakehole for some twenty meters.The dig was apparently abandoned due to problems with spoil removal but the limestone below the grit had been penetrated.

A small cavity also exists high on the north side of the doline above the sink. The sink has evidently formed in a collapsed doline caused by solution of the limestone beneath the gritstone cap rock. The fact that water drains freely (except in exceptional conditions) into this sink indicates that sizable fissures must exist in the limestone. The water has been traced to the Hepste Valley.

It is probable that the sink originated where a -U- type feature collapsed and intercepted a stream which may originally have flowed onwards, south west to sink near Llyn Bach. A optical brightener trace by Roy Morgan proved negative to the long inlet within the new cave at Tir Duweunydd.

References: 12, 14, 15, 18,40.

2. DOLINE (U)

NGR: 94143 12430 Alt. 353m

A collapsed doline in the grit a short distance north of Pwll Derw. It is now quite easy to find as the once dense forest which used to surround it has been cleared. This is probably site ten mentioned by Ockenden in the first edition of this book. There is a possible cave leading down from the western side of this shakehole but it would require a dig for entry.

3. CAVE (U) (S)

NGR: 94126 12492 Alt. 355m L =60m

A shaft at the north east corner of a large doline to the north of Pwll Derw which as with sites one and two is no longer surrounded by forestry. A squeeze through dubious looking boulders at the base of shaft gains a large stepped chamber in grit. This step feature is probably in alignment with the fault which runs through this area. At the bottom of the chamber a small stream disappears into a limestone rift which is much too tight to follow.

4. GREEN CAVE (U) (S)

NGR 94115 12566 Alt. 359m

A large cavern formed in the unconformity just below the boundary fence. As with sites one, two and three this cave is longer surrounded by forestry. A hole on the northern side of the cavern leads to a free climbable descent which is choked at the bottom. This choke has been cleared by Roy Morgan and Tony Donovan to gain an unstable looking chamber.

References: 12,14,18.

5. CAVES (U)

NGR 94090 12731 Alt. 368m

Two caves in a shakehole above the boundary wall. Tight squeeze to southern most cave leads to 10 meters of passage with distinct draught. Hole under boulders in northern leads to 15 meters of passage.

6. PULPIT HOLE

7. DOLINE (U)

NGR 94068 12804 372m

This is an area of collapsed grit a short distance to the north east of pulpit hole.

8. LESSER PULPIT HOLE (U)

NGR 94081 12895 Alt. 382m -see sketch survey.

This cave is situated in a shakehole just below the boundary wall. It is regularly rediscovered by each generation of cavers who claim it as their own. The entrance drops immediately into a chamber. In one corner of the chamber is a nine meter pitch, obscured by a large boulder deposited there by a clumsy caver.

At the base of the pitch, a further seven meter descent gains a rift orientated in north/south direction. Both ends of the rift quickly become too tight but there is a hole at the bottom of the second pitch, which carries a draught.

References: 12,14,18,21,43.

9. GWAEN CEFN-Y- GARREG SINK (U)

NGR 94081 12955 Alt. 390m

An conformity doline with a rowan tree just above the wall taking a small stream which sinks at the base of a small cliff. No cave accessible at present but Charlie Peacock reports entering a cave at this site in the past.

An entry in the Croydon log book reports a bouldery bedding type cave with broken, muddy 35ft pitch with sound of trickling water at bottom. Entrance was on right side of cliff face.

.

References: 12,14

10. CAVE (U)

NGR 94063 13021 Alt.387m

Squeeze in boulders at base of crag leads to a small chamber. There is a slight draught at the entrance. This is site three in the first edition of this book.

Reference: 12

11. ROCK SHELTER (U)

NGR 94072 13132 Alt. 385m

Water sinks into base of rockshelter below overhung cliff face. Any very small holes going off have been blocked up. This site is probably U5 in the first edition of this book and site 27 (NGR 9407 1313) in reference18.

12. CAVE (U)

NGR 94081 13165 Alt. 402m Length approx. 5 meters

Water from cliff sinks into drippy overhang cave in grit. Short entrance drop leads into boulder strewn rift running parallel to the cliff face. Light penetrates from another hole further along the cliff. There is a choked hole at the back, which seems to offer the only hope of a way on.

13.ROCK SHELTER (U)

NGR 94083 13185 Alt. 399m

Drippy overhang with small choked hole at back.

14. CAVE (U)

NGR 94075 13201 Alt.--- m Length approx. 2 meters.

Cave at bottom of cliff is low flat out bedding development, which quickly becomes too tight.

15. CAVE (U)

NGR 94097 13244 Alt. 392m

Flat out crawl at base of cliff leads to three way junction. The passage that goes straight ahead ends almost immediately. The other two passages run parallel to the cliff face. The right hand branch goes to another small entrance while the left- hand branch has a vocal connection with site 16.

16. OGOF PERIGLOR (U)

Alt. Name: Sparking Rocks Cave

NGR 94106 13256 Alt. 402m L=55m VR=13m

This cave is situated a short distance to the south of the gulley which cuts through the Gwaen Cefn-y-Garreg cliff. A flat out crawl reaches a junction beyond a squeeze. The right hand branch goes to a small chamber and rifts while the left goes to a 3 meter pitch which enters the side of the larger Paprika passage which is reknowned for its bright red ochre. Both ends of Paprika passage end in chokes while two loose holes in the floor have been descended and do not appear to offer a way on. Plymouth Caving Group who were the first persons to survey this cave gives the grid reference as 9410 1328.

Reference: 44.

17. OGOF Y TYMESTL EIRA (U)-see survey.

NGR 94124 13305 Alt. 405m L=20-30m

This cave is situated a short distance to the north of the gulley, which cuts through the Gwaen Cefn-y-Garreg cliff. Obvious entrance drops into large boulder breakdown passage running parallel with the cliff face. A window at the end of the first section of passage gains a continuation, which soon chokes.

Reference: 44.

18. CAVE (U)

NGR 94138 13375 Alt. 406m Length approx. 20 meters.

This cave consists of a crawling size bedding which runs parallel to the cliff face. Light penetrates from another possible entrance.

19. CAVE (U)

NGR 94141 13397 Alt. 407m

Cave under prominent ivy bush. Possibly the shortest through trip in South Wales.

20. DIG

NGR94176 13468 Alt. 420m

Small hole blocked with rocks, situated to the north of second gulley, which cuts through the Gwaen Cefn-y-Garreg crag.

21. CAVE (U)

NGR 94162 13478 Alt. 423m

Rock blocked entrance leads to about seven meters of flat out bedding passage. At this point there is a possible cross passage but the floor will require digging out for entry.

22. CAVE (U)

NGR 94169 13508 Alt. 420m

Another flat out bedding , close to sites 21 and 23 which becomes too tight after about 7 meters. This one shows signs of being used as an animal's den.

23. CAVE(U)

Blocked entrance a few meters to the north of site 22. Squeeze at entrance rises up into very small chamber.

24. OGOF GWAEN CEFN-Y-GARREG

Alt. Name Gwaen Cefn-y-garreg Rock Shelter

NGR 94207 13381 Alt.431m L=5m

This site was formerly site one in the previous edition of this book and can be identified by Rowan trees growing in the entrance.It is a large rock shelter formed entirely in gritstone in the side of a collapse doline on the escarpment to the east of the Gwaen Cefn-y-Garreg cliff face. The cave has been formed by the collapse of the surface moor into a cavity in the limestone some 10 meters lower down. Thomas (23) imputes some very large dimensions of the initiating cavity.

References: 12,14,15S,18.

25. OGOF PIODEN

NGR94704 14007 Alt. 435m

This and the following five sites are in fairly close proximity to one another. It seems possible that they were once all part of the same system but due to erosion and glacial in filling have become separated. The rest of Mynydd y Garn seems, with the exception of Hernia Hole and Ogof Carn- y- Botel, singularly devoid of caves and spelaeological features. Due to the presence of some very large shakeholes on Mynydd y Garn it seems likely that there is cave development at depth. As there no localised sinks it is assumed that water enters any cave via a mass of small percolation fissures which are much too tight for a caver to follow. Description........

26. DEER CAVE-see survey.

NGR94654 14011 Alt.438m L=44m

This cave is in two distinct parts. The eastern passage gains a walking /stooping size passage which very quickly ends in a mud dig. The western limb starts as a passage 1.5 meters wide by 1meter high which quickly becomes low at a dig. A draught in this section of the cave seems to suggest a surface connection where the Carn- y-Goetre ridge drops away. The cave gains it name from a red deer antler which was found to one side of the entrance rubble slope.

Mel Davies on examining photographs of the bones found thought they were late neolithic or early bronze age. The original antler is now in Adrian Paniwnyk's possession.

References: 45,46

27. SOLSTICE CAVE

Alt. Name Cave of the little day

NGR 94587 14032 Alt. 437m Length approx. 10m.

This cave gains its name from the fact that it was discovered on the day of the winter solstice 1992. Thrutchy entrance at bottom of bracken filled shakehole gains medium sized chamber. Right hand branch from chamber quickly becomes choked with glacial in fill while left hand branch has voice connection with nearby shakehole.

References: 46

28. MYSTERY CAVE

NGR.......Alt........

This cave which is exceptionally difficult to find consists of a network of small phreatic tubes. Diggers unknown, who left behind them a motley assortment of homemade digging utensils, have exhausted any possible leads.The author failed to locate this cave a few years ago.

29. DIG

NGR 94618 14060 Alt. 437m

1.8 meter deep shaft with balk of rotten timber over the top.

30. DIG

NGR 94771 14166 Alt.14166

Possible dig at the base of a small cliff.

31. HERNIA HOLE

NGR 94664 14392 Alt. 448m

Five meter deep shaft in base of small shakehole becomes too tight at base. Does not look very hopeful.

33. OGOF CARN -Y- BOTEL

NGR 95562 14078 Alt. 432m

This cave is probably associated with the Hepste valley being some distance away from the sites mentioned previously. However, as it is unlikely to be included in another text at present it has been decided to mention it here. A ten meter shaft leads to a rift running in two directions at the bottom. The down dip passage ends in a steeply inclined rocky tube which does not look too hopeful. On the right hand side of the down dip passage a mud choked tube leads off which has received a bit of digging attention. The up dip passage gains a bell shaped chamber decorated with stalactites and with a white and yellow calcite floor.

A site called Carn-y-Botel Pot (SN 9557 1439) mentioned by Stratford (14) could not be found.

Reference: 47

34. GOETRE SPRING (R)

NGR SN 9375 1420

A strong spring in wet weather is situated below the road north of Garreg Fawr Farm. The souce of the water is unknown.

35. FFYNNON GARREG FAWR (R) see page -- for survey.

Alt. Name: Rovers Cave, Ogof Garreg Fawr

NGR SN 9379 1387 L=500m

An extensive cave which runs into the hill below Garreg Fawr Farm. A stream resurges from the cave, which is used as a water supply. It is for this reason that there is no access to this site. It consists mainly of constricted waterlogged bedding planes with little sign of fossil development. The entrance was opened up in 1969 using explosives. A tight squeeze leads to a series of sumps that can be by-passed until a terminal sump is reached about 500m from the entrance. A tributary joins the main stream near the end of the cave. As access has always been denied this cave probably remains partly explored. The source of the water is not known and there is no clearly identifiable sink that can be associated with the resurgence. It seems likely that the water is mainly percolation water collected from a wide area.

Reference: 2,7,11,14,18,40,42.

36. SINK (S)

NGR SN 9337 1278 no GPS

Water overflowing from Llyn Bach sinks into a series of mud floored shakeholes.

37. SHAKEHOLES

NGR SN 9370 1300

Region of shakeholes in the same field to the north east of site 14. A visit on 2/2/1990 revealed one shakehole here with a 4 meter shaft at the bottom of it. A subsequent visit in 2006 revealed that this was now half filled in.

38. OGOF COEDEN PROP (U)-see survey.

NGR SN 93262 12241 L=60m VR=20m Alt. 315m

This cave is entered from the most northerly of the line of shakeholes which lie along a fault above Cwm Porth Farm. It is now difficult to find as it is surrounded by dense forestry. According to reference 18 it derives its name from a Y-shaped dead hawthorn tree, lying in the floor of its shakehole which resembles the kind of old wooden prop used to support a clothes line. On a recent visit no sign of the dead tree could be located -presumably it has rotted away totally.

The entrance leads to a bedding cave between the grit and limestone. A number of blind pits punctuate the floor. In the base of these pits are found a number of static pools the level of which varies according to weather conditions. On a visit by the Adrian Paniwnyk in 2006 after heavy rain, water was noted flowing into the entrance, however, rather contradictinly reference 46 says the shakehole in which Ogof Coeden Prop takes a stream which does not appear to flow directly into the cave.

References: 9,11,12,18S, 40,46.

39. OGOF GANOL (U)-see survey.

NGR SN 93259 12233 L=6m Alt. 312m

A short cave in the Post-Dinantian unconformity with no vertical development. The cave is situated in a separate shakehole a short distance to the south of Ogof Coeden Prop and also lies on the north/west trending fault which passes through the area. It takes water during heavy rain

References: 9,11,12,18S,40,46.

40. OGOF FFYNNON (U) (O) see pages .. and.. for surveys.

Alt. Name: Ogof Ffynnon Fach

NGR SN 93400 12033 L =1000m VR= 30m Alt. 311m

The most southerly of the unconformity caves entered from a large shakehole situated on the same north/west trending fault as sites 38 and 39. The cave has an impressive entrance on the east side of the shakehole which leads to a collapse chamber under the grit. From the chamber a northerly trending passage ends at a squeeze and a climb down the boulder filled plane of the fault. At the bottom of the rift there are two ways on. To the north a crawl enters a large chamber floored with large boulders. An iron ladder may be climbed 5m to gain access to the the continuation of the fault at roof level. This passage passes below two avens and ends.

The south route leads, via a flat out crawl, to another long boulder chamber with a few straws. A narrow drop in the floor of this chamber leads down amongst very unstable boulders until an exit is made from the base of choke into an impressive stream passage in white limestone- totally unlike the rest of the cave until now.

The dangerous nature of this choke was highlighted on 28th. October 1993 when it decided to collapse (again) and trap Eric Downer whilst on a surveying trip. A boulder which had pinned his foot was not released without some difficuty and risk.

Sadly the large passage is short lived, the stream disappearing into the base of the choke you have just been through, whilst a body sized tube which takes some of the main stream quickly becomes too tight. Upstream the passage narrows to reach a sump. This sump is known to dry out after prolonged periods of cold weather or summer drought. When open, this sump leads to an extension which can be followed for about 500m. A succession of muddy and constricted crawls and chambers lead to a 6m pitch and 30 m beyond that a boulder ruckle and parallel squeeze which have not been passed. Reference 48 reports that these obstacles would probably yield to some determined pushing, the most promising being the boulder option with a strong winter draught blowing into this. Much of this passage appears to be fault-guided aligned along the 330-150 degrees axis of the fault on which the entrance lies. A major shale band appears to be the primary stratigraphic control.

The upstream extension in Ogof Ffynnon resurges a large quantity of water in wet weather. In these conditions it is clear that the whole length of the extension sumps. The source of this water and its point of ingress into Ogof Fynnon is not known, although Peat (41) suggests that some of the water might come from Pwll-y-Phaiadr -see site 42. Water sinking at the entrance and that from the upstream extensions is next seen some 100m lower down in the Cwm Porth Inlet of Porth-yr-Ogof.

References: 9,10,11,12,14,18S,37,40,41,48.

41. SINK(S)

Alt. Name Ogof Ffynnon sink

NGR SN 93579 12181 Alt. 329m

A small stream sink in a collapse doline in the gritstone adjacent to the old tramway. Stratford lists this site as Ogof Ffynnon Sink NGR 936 122, although the water which sinks here has not been traced to Ogof Ffynnon which is some distance away.

42. PWLL-Y-PHAIADR (S) (U)

Alt. Name:Pwll Coed-y-Phaiad, Pool Swallet

NGR SN 93678 11908 Alt. 320m

A large collapse feature which due to clearance of the forestry can be seen (2006) from the track which runs towards Sgwd yr Eira. The hour-glass shaped depression takes a stream from the south east and another from the north. The sothern part contains a permanent lake which overflows to sink in the slightly lower northern part. Above the sink there is an alcove amongst unstable looking gritstone blocks. The destination of the water is unknown although Peat (41) suggests that it might be Ogof Ffynnon.

References: 12,18,41.

43.CWM PORTH CAVE (U)

NGR SN 9298 1213 Alt........

This cave is located at the head of the head of the small valley running down to Cwm Porth Farm. A small stream falls over gritstone cliff to enter a cave. Drops straight away onto pitch head. Needs further investigation.

44. CWM PORTH WELL(R)

NGR SN 9294 1221 Alt......

This spring is used as a water supply to the farm just down the dry valley from Cwm Porth cave and is believed to be the resurgence for the water.

45. CWM PORTH CAVERNS

This complicated area is currently under investigation. The problem here is that previous descriptions do not appear to relate very well to what is on the ground!

46. SINK (U)

NGR SN 92800 11592 Alt. 257m

A large collapse doline on the unconformity which takes a stream from the hillside. This is site 23 in the previous edition of the book. Reference 18 lists a swallet at NGR 9292 1158 (site 3) as nothing was found at this particular grid reference it is assumed that site 46 and 3 are one and the same.

Reference: 18.

47. SINK

NGR SN 92766 11505 Alt. 256m

A sink located just above the wall near a derelict barn. This is site 24 in the previous edition of the book and is a sink rather than a spring. This is probably the most southerly of the 'U' type features along the gritstone boundary.

Reference: 18.

48. RISING(R)

NGR SN 92767 11836 Alt.251

Rising in Cwm Porth wood 20m to the east of the track and down hill from Waterfall cave According to reference 18 it receives water from Waterfall Cave.

49. RISING(R)

NGR SN 92734 11656 Alt. 248m

A stream emerges from boulders and flows west to join the Mellte. Reference 18 states the water comes from Waterfall Cave and also site 3 in this book.

Reference: 18

THE SITES ALONG THE AFON MELLTE

50. MORGAN'S HOLE (S) (O)

Alt. Names: Mellte Top Sink, Ogof Mellte Uchaf.

NGR SN..................Alt.................L=30m

The entrance is a small stone slab covered hole in the eastern bank of the Mellte just above the stream. The entrance squeeze leads to a drop at the bottom of which is a small silted stream passage. Upstream leads to a small chamber beyond, which is a too tight rift blocked with a boulder. Down dip from the entrance gains a small phreatic tube that has been cleared of sediment. After about 10m the tube becomes too tight but flowing water can be heard ahead. No draught can be detected at this point and it seems likely that the cave is approaching a sump.

The Mellte can be seen to sink both into its bed and into the bank immediately below the entrance. Water also sinks in the river bed at other locations directly upstream of the cave. Reference 35 states that the water sinking here has been traced to Porth-yr -Ogof (Tradesman's Entrance) in less than 19 hours.

The charcoal bags used in this trace where very peaty and it was suggested that a substantial proportion of water was derived from the grit-capped moor land to the east.

51.CHURCH SINK(S) -see surveys.

Alt. Name: Mellte Main Sink

NGR SN 93160 13224 Alt.260m L=20M+

This is the main sink from the Afon Mellte and engulfs its entire flow in dry weather. It lies just to the north of the Penderyn - Ystadfellte road in the east bank of the stream where the water sinks at various points around a bluff of exposed rock which protrudes into the river bed. During dry weather Croydon CC have dug into short lengths of tight bedding plane and phreatic type tubes. A passage entered in the 1990's possesses a strong outward summer draught and ends in a small boulder chocked chamber.

However, in 2004 a vocal connection was gained with a hole on the surface from this chamber so it is not sure that the draught is just a short circulation draught- see 2004 survey. It is presumed that the series of passages entered by F.Thompson during the drought of 1976 are entered from the passage marked very low silted on the 2004 survey. However, these have not been reentered since the 1970's mainly due to the fact that access would require digging out and that Church Sink is flooded most of the time. It is interesting to note that sections of the walls of the passage entered in 2004 have been raised into small (approx.2cm) high pyramids, presumably caused by fast flowing water.

In wet weather the stream backs up at Church Sink very rapidly, demonstrating the limited capacity of the entrance passages of the sink. The river may then flow in the surface bed as far as Porth yr Ogof or it may sink in a series of ill-defined points in the stream bed between Church Sink and Porth yr Ogof depending on the volume of water in it.

The water from Church Sink reappears in the upstream sumps of Porth yr Ogof after 2.25 hours (Ref.40), having traveled a straight line distance of some 700m.

References: 2,4,5,12,13,14,40,44,49.

52. DIG(O)

NGR SN 92890 12660 Alt.240m

Boulder ruckle at the front of the old river terrace cliff upstream of Porth-yr -Ogof shows signs of acting as a sink/resurgence in flood conditions. Scalloping can be seen on some of the rocks indicating water flow in the past. Digging here might give access to passages upstream of the Top Entrance sumps in Porth-yr Ogof, although permission to dig here is unlikely to be given.

The site is possibly a disused river sink. At least two other similar sights can be found along the river cliff, although these others look less promising.

53. SHAKEHOLE

NGR SN 92912 12553 Alt. 229m

Depression in wooded area between Porth-yr Ogof Top entrance and site 52. Believed to lie close to the diver's passage

54. PORTH-YR-OGOF(S)(R)(O) see page ... for survey

Alt Names: White Horse Cave, Cwm Porth Cavern

L=2220m VR=6m Main Entrance to Resurgence

NGR of the eight principle entrance areas

(a) Main Entrance SN 9281 1241

(b) Resurgence SN 9272 1221

(c) Top Entrance SN9288 1253

(d) Cwmbran Entrance &Dig SN9285 1250

(e) Tradesman's Entrance SN9284 1245

(f) Maze Entrance SN9278 1242

(g) Right Hand Series Entrances SN9278 1237

(h) Downstream Entrance SN9274 1227

This is the principle cave system in the Mellte Valley being part of the main underground conduit of the Afon Mellte itself. Details concerning the hydrology of the cave were discussed in Part 2 of this book. No fewer than fifteen entrances to this system which were coded A-N by the UBSS in the most comprehensive study of this cave (Ref 13). To simplify this matter a little, the individual entrances can be grouped into eight locations as follows:

(a) Main Entrance(UBSS E)

This is the huge natural arch 17.5m wide and 5m high at the base of a cliff into which the river bed leads. It is only in wet weather, however, that the main river flow sinks here; the only water entering the system in normal conditions being that which emanates from Porth-yr Ogof Rising just upstream from the entrance. This entrance gives access to to an impressive through system about 270m long.This starts as abroad, boulder filled cavern which leads to the main canal, adeep water filled, passage 80m long. This in turn leads to the main bedding cave which has a boulder floor and alow roof which spans as much as 30m.

This part of the cave becomes intermittently strewn with tree trunks and other debris which has been washed into the cave in flood. A major inlet joins the main stream just upstream of the the main bedding cave.

(b) Resurgence(UBSS K L M &N)

WARNING: DO NOT ENTER THE RESURGENCE UNLESS YOU ARE WEARING A WET SUIT OR LIFE JACKET

After the bedding cave the main stream flows into a deep pool just inside the downstream exit of the cave. The stream issues over a mall waterfall before resuming its normal surface course. In normal condition small air space exists above the water allowing a 'swim through' to the outside. The exit is about 7m deep and contains undercurrents that have contributed to several fatal accidents at this location. Above the resurgence a low bedding can be entered giving access to a rift that runs parallel to the main stream. This can be followed back to rejoin the main bedding cave above the exit pool.

(c) Top Entrance (UBSS A)

A small cave in the east river bank leads quickly to a sump which has been dived to aseries of upstream sumps, bedding developments and submerged potholes.

Progress upstream towards Church Sink is not yet exhausted but at present this is divers' territory only.

(d) Cwmbran Entrance (UBSS B)

An inconspicuous wet entrance at the base of the cliff in the east bank of the river leads to a sump which connects upstream to the Top Entrance and downstream to Trademan's Entrance. It operates as a sink when the river is high. On the bank above this entrance was another small, unstable cave which collapsed on 4/7/80 causing a serious accident.

(e) Trademan's Entrance (UBSS C)

This name has been applied to several entrances to Porth-yr Ogof in the past but seems to have stuck more firmly to this one which is also known as Entrance No 1. It is located at the base of an impressive cliff to the east of the Main where a moderately large entrance gives access to the underground steam as it imerges from the upstream sumps. This feature has apparently been formed by the partial unroofing of the stream passage by the progressive collapse of the sides of the main river gorge. This alcove in the cliff may have also been at one time have been the main sink.

Downstream the tunnel can be followed in fast flowing water to a sump just before its junction with the main cave a short distance inside the main entrance. A series of bedding developments and sand chambers interconnect between the streamway and the main cave.

(f) Maze Entrances (UBSS D1 and D2)

In the steep cliff at the west side of the main entrance, a number of enlarged joints give access to an extensive three dimensional maze. The lowest level of the maze consists of a complex of sandy passages with pecolation water entering from the west side of the valley.

(g) Right Hand Series Entrances (UBSS F G and H)

A series of avens have breached the bottom of the dry river gorge above the main cave. They can be descended to reach the lower reacches of the maze and a large dry oxbow which is a bypass to the main stream canal. One entrance is free climbable, the other two require 15m of ladder.

(h) Downstream Entrance (UBSS I and J)

These are sometimes known as Trademan's Entrance (see (e) above). They are two large collapse features formed along the line of a fault in the dry river bed above the cave giving direct access to the main bedding cave.